Web fonts are pretty small and only load if used, and loaded only if they're not cached. It's definitely added requests, but those can be deferred intelligently.
Reflowing is preventable using modern techniques, but honestly it doesn't seem like that big of a deal. The tradeoff is you get access to lots of different type options. More type options means more you can convey with type, which is a good thing for people who need to communicate on the web. It's more than just marketing sometimes.
